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The solution conformation of malformin A
Author(s) -
Tonelli Alan E.
Publication year - 1978
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1978.360170506
Subject(s) - chemistry , conformational isomerism , intramolecular force , steric effects , crystallography , amide , nuclear magnetic resonance spectroscopy , dipole , stereochemistry , molecule , organic chemistry
Abstract Solution conformations of the cyclic pentapeptide plant‐hormone malformin A, whose conformational freedom is constrained by an intramolecular disulfide bridge, are derived and presented here. The nmr and CD data of Ptak are used to place restrictions on the search for possible malformin A solution conformers of low energy. Only two distinct conformers were found to be consistent with Ptak's data. Both structures are characterized by an internally buried (solvent‐shielded) D ‐Cys 2 amide proton, a seven‐membered (1–3)hydrogen bond between (N–H) D‐Leu 4and (OC) D‐Cys 2, and a disulfide bridge conformation with a P chirality as manifested in the nmr study by the temperature independence of the amide proton chemical shifts for the D ‐Cys 2 and D ‐Leu 4 residues and the negative sign of the long wavelength maximum in the CD spectrum, respectively. Inspection of space‐filling molecular models of both structures indicates severe steric barriers to their rapid interconversion. Thus, it appears that only one of the two conformers may be present in solution. The difference in their calculated dipole moments (4.6 and 6.9 D ) suggests an experimental method for distinguishing between the two proposed solution structures.